Fluorescent lamps include filaments or electrodes at each end of a glass tube, an ionizable gas and a phosphor coating on the inside of the glass tube. When current is supplied to the filaments, a voltage is induced, ionizing the gas and forming an electric arc between the filaments. The electric arc generates a flow of electric current through the ionized gas causing electrons to be excited and producing light emissions. Typically, the filaments are coated with an emission mix to facilitate electron emission. The use of a ballast in a fluorescent lamp system extends the life of the lamps by preheating the filaments to mitigate the depletion of the emission mix coating.
A lamp reaches an end-of-life stage when the emission mix becomes depleted on a filament causing the lamp to draw more voltage to continue normal operation. This higher voltage results in an increase in lamp temperature which may damage the lamp or the lamp socket.
Conventionally, when an end-of-life stage is detected in one of the lamps, a lamp control circuit would disengage power from all the lamps in the system. This prevents a visual detection of the lamp that has reached the end-life-stage which is undesirable for replacement.
An alternative to disengaging power from all lamps in the system is to include a lamp signal detector and circuit driving elements for each lamp. When an end-of-life stage is detected in a lamp, then only that lamp is disengaged from the power. However, this configuration will not work for a lamp system connected in parallel. It also adds additional cost and complexity.
In addition, traditional ballasts are configured to be used in a lighting system having a uniform lamp type. This means that ballasts must be changed every time a lamp type changes. With the constant improvement of lamps, upgrading to a new ballast is costly and inefficient.